Since the early 1980s, adjustable gastric bands have provided an effective alternative to gastric bypass and other irreversible surgical weight loss treatments for the morbidly obese. The gastric band is wrapped around an upper portion of the patient's stomach, forming a stoma that restricts food passing from an upper portion to a lower portion of the stomach. When the stoma is of the appropriate size, food held in the upper portion of the stomach provides a feeling of fullness that discourages overeating. However, initial maladjustment or a change in the stomach over time may lead to a stoma of an inappropriate size, warranting an adjustment of the gastric band. Otherwise, the patient may suffer vomiting attacks and discomfort when the stoma is too small to reasonably pass food. At the other extreme, the stoma may be too large and thus fail to slow food moving from the upper portion of the stomach, defeating the purpose altogether for the gastric band.
An artificial sphincter may be utilized in any number of applications within a patient's body where it is desirable to vary the size of an orifice or organ. Depending upon the application, artificial sphincters may take the form of a flexible, substantially non-extensible band containing an expandable section that is capable of retaining fluids. The expandable section would be capable of expanding or contracting depending upon the volume of fluid contained therein. One particular example of an artificial sphincter is an adjustable gastric banding device, such as described in U.S. Pat. Nos. 4,592,339; 5,226,429; 6,102,922 and 5,449,368, the disclosure of each being hereby incorporated by reference. Adjustable gastric band implants have a hollow elastomeric balloon with fixed end points encircling a patient's stomach just inferior to the esophago-gastric junction. When saline solution is delivered into the hollow balloon, the gastric band swells and constricts the stomach, for example, for obesity reduction. Different degrees of constriction are desired, and adjustment is required over time as the patient's body adapts to the constriction.
Adding or removing saline solution from the adjustable gastric band is typically accomplished by injecting through a fluid injection port to achieve a desired diameter. Since adjustable gastric bands may remain in the patient for long periods of time, the fluid injection port is typically installed subcutaneously to reduce the likelihood of infection. Adjusting the amount of fluid in the adjustable gastric band is achieved by inserting a Huber tip needle through the skin into a silicon septum of the injection port. Once the needle is removed, the septum seals against the hole by virtue of the compressive load generated by the septum. A flexible conduit communicates between the injection port and the adjustable gastric band.
While subcutaneously implanted injection ports are a successful approach to readily adjusting a gastric band, and are a desirable feature to retain for initial installation or as a backup, it would be desirable to remotely adjust the gastric band. While minimally invasive, insertion of the Huber needle to adjust the saline solution volume does introduce increased risk of infection. In addition, this procedure typically entails the inconvenience and expense of scheduling time with a surgeon.
Some pumping methods suffer from a small amount of leakage across the pump. For example, in an implanted peristaltic pump, such as described in U.S. Pat. No. 6,102,678, a piezoelectric drive system is used to provide a rotary device that is lightweight and compact with a very small axial volume. While leakage may be of no consequence in an infuser intended to dispense fluid when the amount dispensed is measurable, the leakage may be extremely inconvenient for maintaining a constant fluid volume over an extended period of time to maintain an artificial sphincter.
Implantable infusers that contain a metal bellows accumulator are known for such uses as dispensing therapeutic drugs, such as described in U.S. Pat. No. 4,581,018. One common drawback is that implantable infusers are designed for one way controlled dispensing. Refilling the reservoir typically requires insertion of a syringe into a septum.
In an afore-mentioned co-pending application entitled “PIEZO ELECTRICALLY DRIVEN BELLOWS INFUSER FOR HYDRAULICALLY CONTROLLING AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Ser. No. 10/857,315, an advantageous infuser containing no ferromagnetic materials provides an accurately controllable volume of fluid to a closed gastric band capable of bi-directional adjustment of the fluid volume. The infuser has a titanium bellows accumulator, which may be collapsed or extended to positively displace fluid accumulated therein, thereby serving as both a reversible pump and reservoir. Thereby, a bi-directional pump that is practically immune to external magnetic fields is achieved. Such an implanted device may be used during Magnetic Resonance Imaging (MRI) without damage to the device or patient.
While this piezo-electrically driven infuser has many advantages for certain applications, it would be desirable in some applications to further reduce the size of the infuser to increase patient comfort and acceptance of the implant. In particular, it would be desirable to eliminate or greatly reduce components that surround the metal bellows accumulator while enhancing the long-term reliable performance.
Consequently, a significant need exists for a remotely controllable, bi-directional infuser that reliably locks at a selected fluid volume between adjustments.